Study of composite fuzzy control of dissolved oxygen in a sequencing batch reactor pilot process of synthetic papermaking wastewater

The studies on the automatic control strategy of papermaking wastewater treatment process have always been sparse for a long time. During the process of treatment, the oxygen concentration in the wastewater is a key substrate in animal cell metabolism and its consumption is a parameter of great interest for the monitoring. This paper introduces an effective and robust control strategy to control the dissolved oxygen concentration in a pilot sequencing batch reactor of wastewater treatment process. For comparison, four control strategies are tested and evaluated: ON/OFF, PID, fuzzy and composite fuzzy control strategies. The control results with composite fuzzy control strategy show that, the controlled dissolved oxygen concentration is around the set point with 0.05 standard deviation and 3.5 minutes rising time, but the good controlling performance is obtained at the price of relatively high aeration volume for the heavier pollution load. It takes less time than that of the other strategies to arrive the ammonia valley, which shows its good ability of chemical oxygen demand removal. From the compared results of these four control strategies, we can conclude that the proposed composite fuzzy control strategy is proved to be a robust and effective controller for the DO concentration of synthetic papermaking wastewater.